1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method, and, in detail, to image processing technology for detecting tampering made to an original document.
2. Description of the Related Art
Along with enforcement of the Electronic Document Law, established in Japan, November, 2004, it is expected that occasions of storing paper documents in a form of electronic data will increase accordingly. According to the Electronic Document Law, it is allowed to store a document, which ought to be stored, in a form of electronic data. According to the law, image data, obtained from being read from a paper document by means of a scanner or such, is regarded as an original document when specific requirements are met. As a result, it is expected that the costs required for printing, circulating and storing documents, business forms, and so forth, required for proceeding with business, will be remarkably reduced, and thus, computerization of inter-enterprise business transaction will be further promoted.
From the establishment of the Electronic Document Law, the costs required for storing and managing paper documents are reduced as a result of the paper documents being read by a reading apparatus, thus corresponding electronic data being obtained for being stored, and the original paper document being discarded. However, at the same time, a danger of being subject to tampering increases accordingly. There may be a case where a paper document before being read by a reading apparatus is tampered with, or, another case where tampering is made on electronic data obtained as a result of a paper document being read by a reading apparatus. For the latter case of tampering, the danger may be eliminated with the use of a time stamp system employing enciphering technology. Specifically, tampering can be detected as a result of signature data, which can be created only from a secrete key, being verified. For the former case of tampering, detection thereof is easy when the paper document is such that some physical trace is necessarily left when tampering is made. However, from electronic data which is obtained from being simply scanned by means of the reading apparatus, such trace may not be easily detected. Since the original paper document is discarded after being read by the reading apparatus as mentioned above, tampering should be detected only from the corresponding electronic data. Technologies have been proposed to detect tampering from electronic data.
For example, according to Japanese Laid-open Patent Application No. 11-039468 (referred to as a patent document 1, hereinafter), electronic data is obtained as a result of light, which transmits through a paper document, being read in a condition in which the light is applied from the reverse side of the paper document. A part of the paper document, for which a paper piece is attached to the obverse side thereof (i.e., cutting and attaching tampering), or tampering with the use of correcting fluid, has its transmittance reduced accordingly, and thus, the tampered part has darker image data, and thus, the tampering can be easily detected from the electronic data.
As anther related art, a technology called ‘digital watermarking’ exists. According to this technology, other information (message authentication code) is obtained from information (message), and is printed out on a paper document, according to a predetermined rule. And, the message authentication code is printed out as the message together. Then, when both of the information is proved as being produced according to the predetermined after they are transformed into electronic data by means of a reading apparatus, it is determined that tampering has been made. For example, a background pattern (message authentication code) is selected from hash function values (i.e., the predetermined rule) of character data (message) of the document, and then, the characters and the background pattern are printed out in combination. That is, when a tampering person tampers with the characters themselves of the thus-obtained paper document, it may be difficult to also tamper with the background pattern in such a manner that both meet the predetermined rule relationship, since the background pattern may be provided throughout a wide range of the paper document, and, also, the background pattern according to the predetermined rule may not be created when the predetermined rule is not published. As a result, the tampering can be detected.
Further, ‘shade detection’ technology exists, as another method. According to this technology, as disclosed by Japanese Laid-open Patent Application No. 11-041450 (referred to as a patent document 2, hereinafter), the above-mentioned cutting and attaching tampering is detected from shade included in corresponding electronic image data. That is, irradiation light of a scanner is reflected in a direction other than that toward a sensor due to a step created in the periphery of the cut and attached tampered part. As a result, a dark shade occurs at this part. From such unnatural shade, the tampering is be detected.